Adnan al-Damiri, Jenin's police chief, accused the Israeli army of targeting its officers and held it responsible for the ongoing escalation in Jenin.

"Killing the Palestinian policeman means that Israel's escalation does not even rule out the Palestinian security services," al-Damiri said.

Palestinian police consider the Israeli operation an attempt to obstruct its efforts to restore security in Jenin, he added.

School attacked

In Gaza City, three explosive devices were set off in the American International School causing damage but no injuries, Palestinian security sources and witnesses said.

Three explosives devices were set off at the American International School [AFP]

"A large number of masked gunmen attacked the school at dawn. They poured petrol all around and blew up several explosive devices and destroyed some of the premises," Rebhi Salem, the school's director, said.

The armed men said they were part of an al-Qaeda organisation operating in Gaza, he added.

The school is a private institution that is part of an association of "American Schools" in the Middle East. The curriculum stresses English as well as Arabic studies. None of the teachers are American and a US embassy official said the school has no connection to the US government.

Two members of staff were briefly abducted from the school in March 2006.